Electronic timepiece



Sept. 29, 1970 wlGET 3,530,664

ELECTRONIC TIMEPIEGE Filed Nov. 9, 1967 22 7 [8 v If Wis/J1 p T[c] F I G. 3

INVENTOR 5722 0/01 W/G[ a/mi ATTORNEY United States Patent 3,530,664 ELECTRONIC TIMEPIECE Fridolin Wiget, Cortaillod, Switzerland, assignor to Ebauches S.A., Neuchatel, Neuchatel, Switzerland, a

firm

Filed Nov. 9, 1967, Ser. No. 681,626 Claims priority, application Switzerland, Nov. 25, 1966, 17,070/ 66 Int. Cl. G04c 3/00 US. C]. 58-28 1 Claim ABSTRACT OF THE DISCLOSURE An electronic timepiece with an oscillating regulator sustained electrically by a transducer controlled by a signal induced in a pickup coil and amplified by a transistor, wherein the source impedance of the control signal is varied as a function of the temperature so as to compensate the width of the sustaining pulses for the effect of tem erature variation on the operation of the timepiece, a thermistance being included in the control circuit of the transistor to effect this compensation, and the winding of the pickup coil itself optionally being fabricated of a metal with a compensatory thermal coefficient.

BACKGROUND OF THE INVENTION Field of the invention An electronic timepiece with an oscillating regulator member electrically sustained by a transducer controlled by a signal induced in at least one pickup coil, amplified by an electronic circuit comprising at least one transistor.

Description of the prior art The influence exerted on the operation of a watch by temperature variations poses a considerable horological problem.

It has been attempted, in the case of electronic timepieces, to compensate for the effects of temperature variations on the frequency of the oscillator, by acting on the phase of the sustaining pulses. This mode of compensation, currently used, causes a fault of isochronism.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electronic timepiece with a means of thermal compensation applicable equally well to the oscillator as to the sustaining circuit, and which enables compensation not only for the thermal coeflicient but also for secondary errors.

According to the invention, there is provided an electronic timepiece with oscillating regulator sustained by electrical pulses by a transducer controlled by a signal induced in at least one pickup coil and amplified by an electronic circuit comprising at least one transistor, characterized by the fact that the control signal of the transistor has an impedance source which is variable as a function of the temperature, so that variations of temperature are translated by variations in the width of the sustaining pulses whereby the effects of said variations in temperature on the period of oscillation are at least partially compensated.

BRIEF DESCRIPTION OF THE DRAWING The invention will now be described more fully with reference to the accompanying drawings which show schematically, purely by way of illustrative examples, several embodiments of an electronic timepiece according to the invention, and in which:

FIG. 1 is a diagram of one embodiment showing an electronic circuit for sustaining oscillations of the oscillating regulator member of an electronic timepiece;

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FIG. 2 is a diagram showing another embodiment of electronic circuit of an electronic timepiece according to the invention; and

FIG. 3 is a graphical diagram of the operation of a timepiece movement as a function of temperature.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings now and firstly for general considerations to FIG. 3, it will be recalled that, by convention, the thermal coefficient of a timepiece is the variation in operation between two fixed temperatures, divided by the separation of these two temperatures. This coefficient is expressed, graphically, by a line of which the inclination is representative of its value; line a of FIG. 3, in which the operation M, in seconds per day for example, of a timepiece movement, is represented as a function of the temperature T expressed in degrees C., for example.

The secondary error constitutes the difference between the thermal line thus calculated and the .real curve of the operation as a function of temperature, at any given point of the curve. This latter is indicated by b in FIG. 3, and the secondary error by a point P on the temperature axis is represented by the distance d between the line a and the curve b, at the point considered. The thermal coefiicient is expressed in seconds per day and degrees C., and the secondary error is expressed in seconds per day.

The electronic timepiece of which the sustaining circuit is represented in FIG. 1, for example, a wristwatch, is preferably a watch with an oscillating mechanical regulator.

The oscillations of this regulator are sustained electrically by conventional means, comprising at least one permanent magnet borne by the oscillator and being displaced, in the course of oscillations, with .respect to a pickup coil in which it generates, by induction, a signal controlling an amplifying circuit, transistorised, feeding at least one driving coil in respect of which this magnet is displaced, in effect a second magnet borne by the regulator, during the oscillations of the latter. This arrangement being well known, only the electronic circuit has been shown.

This circuit comprises a source of current, for example a battery or an accumulator, of which the two terminals are designated respectively by 1 and 2, the terminal 1 being shown on the drawing as being the ground. The circuit comprises a transistor 3 of which the base, designated by 3B, is connected to the terminal 2 of the current source through'a biasing circuit 4 comprising a coupling capacitance 5 and a bias resistance 6 connected in parallel, and through the pickup coil, designated by 7.

The emitter of the transistor 3, designated by 3B is directly connected to the ground 1, although its collector, designated by 3C, is connected to the terminal 2 0f the current source through two driving coils 8 and 9 mounted in series. A by-pass capacity 10 is interposed between the output of the bias resistance 6 and the collector circuit of the transistor.

A thermistance 11 is connected in series between the output of the pickup coil 7 and the input of the biasing circuit 4. The resistance of this thermistance varies as a function of temperature, which is equivalent to causing to vary, as a function of temperature, the impedance of the source Z of the signal which controls the base 3B of the transistor 3. During each sustaining pulse, the condenser 5 is charged, through the base-emitter diode of the transistor and the source impedance Z of the signal which controls the base of the transistor, to a voltage V Between two sustaining pulses, the condenser 5 is slowly discharged into the resistance 6. If the source impedance Z of the signal increases, the maximum voltage V on the condenser will diminish, due to the fact of the drop in voltage of the charging current of 5 on Z In parallel fashion, if the control signal of the transistor is not steep-fronted, at the moment of release this transistor will be advanced and there will not be an increase in the width of the sustaining pulse in the driving coils 8 and 9. This variation in the width of the sustaining pulse is translated, in its turn, by a variation of the period; that is to say the frequency or the operation of the oscillator.

A tuning fork 18 having two magnets is shown as disposed with one of the magnets 20 oscillating in front of coils 7 and 9 and the other of the magnets 24 oscillating in front of coil 8.

In the same way, if the impedance Z of the signal is reduced, there will be a reduction in the width of the sustaining pulses, and the operation will vary in the opposite direction.

Thus, by judiciously selecting the thermistant as a function of the thermal coefiicient of the regulator to be corrected, in fact of the regulator and of the sustaining circuit itself, there can be achieved a practically total correction of the effects of temperature variation on the operation of the watch. It is sufficient in fact that the correction curve, designated by e in FIG. 3, be symmetrical with the curve b of the variations of the operation as a function of the temperature, with respect to any axis parallel to the temperature axis, so that the sum of the curves b and 0, shown by the line 2 in FIG. 3, is constant.

It is to be noted that the terms thermistance, or thermistant circuit, are to be understood to mean either a thermistance properly so-called, or a thermistance network (NTC and/or PTC), or a network of termistances and of resistances, of which the combination is a function of the operation-temperature relationship, simple or complex, that it is desired to achieve.

A substantially identical result will be obtained by inserting the thermistance 11, or thermistant circuit, at a different point of the circuit indicated at X and num- 'bered 12 in FIG. 2; that is to say between the terminal 2 of the current source and the pickup coil 7. It could be placed at a point between the biasing circuit 4 and the base 3B of the transistor 3.

Finally, it is to be noted that, to make the impedance of the control signal source of the transistor vary as a function of the variations of temperature, the winding of the pickup coil 7 could also be elfected in a metal having a higher thermal coefficient than copper, adapted to the thermal coefiicient of the oscillator that it is desired to compensate. Thus, it Would then be the resistance of the pickup coil itself which would vary as a function of the temperature.

I claim:

1. In an electronic time piece, an oscillating regulator sustained by electrical pulses by a transducer controlled by a control signal induced in at least one pickup coil and amplified by an electronic circuit, the electronic circuit comprising at least one transistor, the control signal of the transistor having a source impedance which is variable as a functionof the temperature with variations of temperature being translated by variations in the width of the sustaining pulses whereby the effects of the variations in temperature on the period of oscillation are partially compensated, the control circuit of the transistor comprising at least one thermistant element producing variations in resistance of the control circuit as a function of variations in temperature, a biasing circuit in the electronic circuit comprising a bias resistance and a coupling capacitance connected in parallel and interposed between the pickup coil and the base of the transistor with thermistant element being located in series with said biasing circuit.

References Cited UNITED STATES PATENTS 3,282,042 11/ 1966 Schaller 58-23 3,293,568 12/ 1966 Ganter et a1. 58-23 X 2,831,114 4/ 1958 Van Overbeek 33 l66 3,333,160 7/1967 Gorski 331-66 FOREIGN PATENTS 47,365 4/1966 Germany.

RICHARD B. WILKINSON, Primary Examiner E. C. SIMMONS, Assistant Examiner US. Cl. X.R. 331--66 

